There are approximately 84,500 to 114,000 new lower-limb amputations each year in the United States. Amputation rates are rising each year, in part because of the rapid increase in diabetes and also because of improvements in treating traumatic injury and vascular disease. More of the patients experiencing these problems are able to live longer but may require limb amputation in order to survive. Further, the recent wars in Iraq and Afghanistan have caused an increase in the number of servicemen and women who undergo an amputation, typically young individuals who are otherwise healthy. Because of the early age at which the amputation occurred, these individuals will be prosthesis users for many years. Thus, there is a strong need to create quality prosthetic limbs for the increasing lower-limb amputee population.
The design of an effective prosthetic socket is crucial to the rehabilitation and overall health of a person with an amputated limb. This point cannot be overemphasized. Most of the time and energy a practitioner applies in making a prosthesis is spent on fabricating the socket that must be fitted to the residual limb. The prosthetic socket must be shaped so that it supports the residual limb in load tolerant areas, while avoiding irritation of sensitive regions on the limb that contact the inner surface of the socket. If these criteria are not achieved, residual limb soft tissue breakdown often occurs when the patient uses the prosthesis. The result of a poor socket fit may include painful sores, blisters, ulcers, or cysts on the residual limb that typically restrict continued prosthesis use, and in severe cases, necessitate a further amputation to a higher anatomical level which can lead to further disability. The incidence of skin breakdown in lower-limb amputees has been reported to be from 24% to 41%. Accordingly, at any one time, as many as 41% of prosthesis users may be experiencing breakdown of the tissue on the residual limb. The principle cause of such breakdown is a poorly fitting prosthetic socket.
Practitioners face challenges in making quality sockets for the increasing amputee population. Also, there is a shortage of prosthetists in the industry, and that shortage is expected to increase in the future, as the demand for prosthetic devices increases. A prosthetist's time is precious and must be used as efficiently as possible. It may be beneficial to improve a prosthetist's efficiency, speed, documentation, repeatability, and quality of fitting a socket to a patient's residual limb, and to ensure a proper socket design early in the process of fitting a prosthetic socket to a recipient.
Modern prostheses are often made using computer-aided-design and computer-aided-manufacturing (CAD/CAM) methods, which were introduced to the prosthetics field about 25 years ago to address these needs. When using a CAD/CAM approach to produce a fitted socket, a practitioner measures the shape of the residual limb using either a cast impression or a commercially-available scanning device that implements one of a number of shape acquisition modalities (e.g., use of a laser scanner, contact hand digitizer, video scanner, structured light projection, or digitization of a plaster cast). The resulting shape is then sent to a custom computer numerical control (CNC) mill, referred to in the art as a “carver,” to fabricate a positive model which is then used to form the socket. The practitioner may design a socket on a computer using one of several commercially available software packages and methods. A thermoformer can be used to vacuum form a socket by heating a polymer cone and then vacuum forming it onto the positive model. Alternatively, a thermoplastic sheet can be draped or wrapped over the positive model. After the edges are trimmed, a completed socket is provided and is tested with the patient to determine the acceptability of the fit.
Other methods for socket fabrication exist, including a novel motion guided extrusion technique (referred to as SQUIRT SHAPE™, at Northwestern University), and other rapid prototyping techniques. However, regardless of the method used for fabricating a socket, there is often a quality control problem that arises in the fabrication process, and means are needed to enable a prosthetic socket designer to determine if the fabricated socket indeed accurately matches the shape that was designed. Currently, practitioners creating sockets often spend too much time fixing or remaking the sockets that were produced incorrectly by the CAD/CAM process or the forming process, or both. The benefits of CAD/CAM system, which include improved efficiency, speed, documentation, and lower expense, are substantially reduced or even lost because of this problem. Prosthetists who have an in-office CAD/CAM system suite, central fabrication facilities, and manufacturers of CAD/CAM equipment used to produce sockets could thus benefit from technology for evaluating the quality of each socket produced, to avoid the expense and delay incurred to fix or remake a socket as necessary to achieve a proper fit with the patient's residual limb.
In recent studies, considerable variability was found in the quality of prosthetic sockets fabricated by central fabrication facilities using computer-socket manufacturing methods. Because fabrication errors are often hard to see by eye, they might not be identified by the practitioner until the socket is test fit to the patient. These errors extend the fitting process because they confound clinical fitting. The prosthetist must correct errors both from faulty manufacturing and from incorrect socket design, and it can be difficult to distinguish between the two. Further, if computer-socket manufacturing errors are inconsistent from one fabrication run to the next and the errors are substantial, a practitioner will have difficulty effectively optimizing the socket shape file. This problem might explain why in computer socket design and manufacturing literature there is a wide range in the number of sockets (1 to 5) reported necessary to achieve an acceptable fit. Particularly for young prosthetists, computer-socket manufacturing errors can add significant challenge to prosthetic design.